Laser apparatus

ABSTRACT

A relatively high-speed optical shutter for use in the optical system of a laser for greatly increasing its peak power output. In one aspect, the optical shutter comprises a system of prisms arranged to cause multiple impingement of the internal laser beam on a rotatable mirror, whereby to multiply the angular sweep rate of the laser beam as it is reflected back into the laser medium. In another aspect, the optical shutter includes a telescope arranged to increase the apparent rotational speed of the mirror, and hence the angular sweep rate of the beam, by magnifying the width of the beam reflected back into the laser medium.

United States Patent 91 Forkner 51 Jan. 16, 1973 [54] LASER APPARATUS3.310,7s3 3/1967 Burkhalter ..331 94.5 3,328,l l2 6/l967 Soules et al.....33l/94.5 [75 Invemm' f f' plymmth Meet 3,315,117 4/1947 Benson..331/94.s

[73] Assignee: Philco-Ford Corporation, Blue Bell, PrimaryExaminer-William L. Sikes Pa. Att0meyCarl H. Synnestvedt [22] F1led: IFeb. 27, 1969 [57] ABSTRACT [21] Appl' 842'036 A relatively high-speedoptical shutter for use in the Related Appncation Data optical system ofa laser for greatly increasing its peak 62 power output. In one aspect,the optical shutter com- D1v|s1on of Ser. No. 346,820, Feb. 24, 1964,Pat. No. prises a System of prisms arranged to cause multiple 3 434971impingement of the internal laser beam on a rotatable mirror, whereby tomultiply the angular sweep rate of "331/ the laser beam as it isreflected back into the laser medium In another aspect, the opticalShutter [58] Field of Search ..33l/94.5, 350/160, 332/751 cludes atelescope arranged to increase the apparent rotational speed of themirror, and hence the angular [56] References cued sweep rate of thebeam, by magnifying the width of UNITED STATES PATENTS the beamreflected back into the laser medium.

9/1966 OKaya ..331/94.5 20 Claims, 14 Drawing Figures Ill IE Gill/[RATOR PATENTED JAN 16 I973 SHEET 1 BF 4 LASER APPARATUS This is a divisionof application Ser. No. 346,820, now US. Pat. No. 3,434,073 filed Feb.24, 1964.

This invention relates to laser apparatus, and more particularly toimprovements in so-called Q-spoiling devices of giant-pulse lasers.

In one known form of laser the working element is a single crystal ofpink ruby in the form of a cylindrical rod, of for example aboutone-half centimeter in diameter and 4 centimeters in length, and havingflat end faces that are plane to a high degree of accuracy. The ruby rodis disposed between two parallel reflecting surfaces, at least one ofwhich may be formed on the end of the rod. One surface is completelyreflecting and the other surface is only partially reflecting. The rubyrod is irradiated, or pumped, laterally of its axis by light from a highintensity light source, such as a flash lamp, operated usually for a fewmilliseconds at a time with an input of relatively high value. Afraction of the energy emitted by the flash lamp is absorbed by the rubycrystal. When the energy absorbed from the exciting irradiation exceedsa certain threshold, and a very short time after the start ofirradiation, coherent radiation emerges in a narrow beam through thepartially reflecting surface which forms one end of the resonant opticalsystem of the laser.

The intensity of the laser beam varies irregularly, it having beenobserved that the time delays between the start of excitation and theonset of coherent oscillations are not uniform in spite of efforts tokeep all experimental variables under control. Once coherent lightappears, its intensity will vary greatly and irregularly with spikes, orpulsations, of durations of about I microsecond.

It is possible to overcome the aforementioned irregularities and toincrease the peak intensity of the output pulse by temporarily loweringor spoiling" the Q of the optical system of the laser. By this so-calledQ- spoiling the laser crystal can be irradiated, or pumped, past thenormal threshold value at which it begins to emit coherent radiation.After the pumping irradiation has attained a condition of saturation,the optical characteristics of the system are again modified by suddenlyraising or, unspoiling, the Q, with the result that a relatively largeburst of radiant energy is emitted by the crystal. For example, aconventional laser system which would normally produce a series ofspikes having a peak power of 50 kilowatts when operated in the mannerjust described may achieve a peak output of 5 megawatts. Systems of thistype are known in the art as giant-pulse laser systems.

Q-spoiling in the optical system of the laser normally is accomplishedby means of a light shutter placed between the ruby rod and one of thereflecting surfaces, or by rotating out of alignment means comprising,for example, a rotating prism/or mirror which serves as the fullyreflective surface for one end face of the crystal. In this system thepumping or irradiating lamp is triggered to flash so that the pumpingbegins just before the shutter is opened, or just before the rotatingreflective mirror or prism is brought into optical alignment with theend of the laser crystal. The amplitudeof the pulse produced isdependent to a large extent upon the rapidity with which the shutter isopened or the reflective surface is brought into optical alignment.

It is an objective of this invention to provide, in a Q- spoiling systemas described, optical means operative greatly to multiply the effectiverotational rate of the reflective means.

It is a further objective of the invention to provide, in a giant pulselaser apparatus, optical means to increase the effective operating speedof the shutter.

The invention contemplates, in one form thereof, that the reflectivemeans comprises a rotating-mirror shutter considerably larger indiameter than the crosssection of a ruby crystal, and interposing atelescope between the rotating mirror and the end of the ruby crystal.In this embodiment the effective rotational rate of the mirror isproportional to the product of its actual rotational rate and themagnification of the telescope.

The invention further contemplates that the laser Q- spoiler maycomprise a plurality of prisms, one of which is rotated. The opticalpath between the two reflecting surfaces of the laser optical system isfolded so that energy emitted by the laser rod is caused to be reflectedby a face of the rotating prism a plurality of times. This may beachieved by means of suitably positioned, stationary reflectors, suchfor example, as roof prisms. The multiple reflections from the rotatingprism have the effect of multiplying the apparent speed of rotation ofthe rotating prisms. Thus an increase in the apparent speed of theQ-spoiling action is achieved advantageously without an increase in theprism rotation rate.

Still further it is contemplated by the invention that theabove-described telescope and rotating prism arrangements may becombined to achieve still faster, high frequency shutter operation.

The invention may therefore be briefly summarized as comprising acombination of: a working element capable of laser action; reflectiveshutter means disposed and adapted to reflect radiation emitted by saidelement back into the latter; means for establishing the operating speedof said shutter means; and means operable optically to modify theeffective operating speed of the shutter. v

For a more complete understanding of the invention, reference may be hadto the following detailed description, taken in light of theaccompanying drawings in which:

' FIG. 1 is a somewhat diagrammatic showing, partly in perspective, ofgiant-pulse laser apparatus embodying the invention;

FIG. 2 is a perspective view, on a reduced scale, of a portion of theapparatus illustrated in FIG. 1, and in which one of the elements hasbeen modified slightly;

FIG. 3 is a plan view of theapparatus illustrated in FIG. 2;

FIG. 4 is a somewhat diagrammatic showing of apparatus illustrated inFIGS. 1 to 3, and demonstrating the optical principles upon which theinvention is based;

FIG. 5 is a further diagrammatic showing of the optical principles ofthe invention;

FIG. 6 is a view similar to FIG. 2 and illustrating a modifiedembodiment of the invention;

FIG. '7 is a view similar to FIG. 6 and illustrating another modifiedembodiment of the invention;

FIG. 8 is a view similar to FIGS. 6 and 7 and illustrating a furthermodified embodiment of the invention; and

FIGS. 9 through 12A comprise additional modified embodiments of theinvention, in which different optical systems are utilized.

With more particular reference to FIG. 1, laser apparatus embodying theinvention comprises a cylindrically formed crystal 10' of suitablematerial, for example pink ruby, having end faces 11 and 12 that areplane to a high degree of accuracy. End face 11 is provided with apartially reflective coating and face 12 has no reflective coating. Ahelically formed Xenon flash tube 13 is coiled about crystal 10, and isenergized by a suitable power supply 14 of known construction. Arotatable prism 15 is drivingly coupled with a motor 16, and a lamp 17isdisposed and adapted to emit a beam for sequential reflections byexternal faces of rotating prism 15 onto a detector 21. Reflections byrotating prism 15 of the light beam from lamp 17 will reach detector 21according to the sequential positional relationships of the outerreflective faces of the prism 15. Detector 21 is constructed andarranged to actuate a pulse generator 22 which in turn triggers powersupply 14, as the face 18 of the rotatable prism reaches the positionshown, in which position said face reflects the beam onto the detector.

As a practical matter, in view of the relatively high rotational rate ofprism 15 and compared with the time required for flash lamp 13 to fire,a typical pulse rate is one per 10 seconds, as may be provided by anoperator who actuates a trigger or push-button switch, such as is seenat 220, to fire the laser. The illustrated synchronizing system, uponactuating the trigger switch, operates to fire as the prism 15 isrotated into beam reflecting position, or just prior to such opticalalignment of prism 15 as to provide for return of the emitted beam tononreflecting end 12 of laser rod 10.

The Q-spoiling means comprises stationary prisms 23 and 24 so opticallypositioned as respects one another and rotatable prism 15, as to providethe illustrated light paths to and from the light transmissive ornonreflective end face 12 of ruby crystal 10', in accordance with thedirectional arrows. It will be appreciated that the complete light pathsexist only for the illustrated position of the rotatable prism 15, justfollowing energization of Xenon lamp 13. The several prisms thereforecomprise the fully reflective means for end face 12 of the laser rod,and as will be described in what follows, rotation of prism 15alternately spoils and restores the Q of the laser optical system.

In FIG. 1, locations of all rays of light entering or leaving the prismsare designated by the letter A. The light rays leaving the end 12 of rod10 are polarized in a vertical plane, and the prism dimensions andangles are selected so that such rays enter and leave at the socalledBrewster angle at which no reflection losses occur for incident lightpolarized in the plane of incidence. The Brewster angles are designatedin FIG. 3 by their actual values, and are based on materials having arefractive index of l.52. However, it will be understood that thesevalues are for illustrative purposes only, and materials having otherrefractive indices may be used.

All reflections inside the prisms are designated by the letter B andoccur at less than the critical angle. Hence, these reflections arelossless, or totally internal. The only losses within the optical systemcomprising the shutter and reflector means are due to the prism materialitself. These losses can be minimized substantially by selecting theproper material for the wave length of the light emitted by ruby crystal10.

It will be noted that the difference between the apparatus illustratedin FIG. 2 and the corresponding apparatus illustrated in FIG. 1 is thatthe ruby rod or crystal 10' shown in FIG. 2 has its non-reflective face12a cut at the Brewster angle, whereas the corresponding face 12 in FIG.1 is cut normal to the major axis of the rod. Also it will be noted inFIG. 2 that the letters A and B have been replaced with numerals 1 to 10that correspond to the sequential paths of the light beam through theprisms, as will be more fully discussed in what follows.

It can be shown, and as will be more fully understood from theequivalent mirror systems illustrated in FIGS. 4 and 5, that uponrotation of prism 15 through a predetermined given angle, beamsreflected, as at points B in this prism, will each be rotated or sweptthrough twice the said given angle. It follows, therefore, that eachreflected beam sweeps at double the rotational rate of the reflectivesurface. Since there are four such reflections, the returning beam willsweep across the end of the laser rod at an angular speed 8 times therotational speed of prism 15.

While the light rays or beams in FIG. 1 and 2 are shown as being spacedfor the sake of clarity in tracing the path of the beam from and to therod in restoration of reflection, or unspoiling of the Q, thecorresponding rays are illustrated as coincident rays in FIG. 3. Rays toeither side thereof also have been included to indicate the limits ofthe lateral disposition of the rays.

With particular reference to FIG. 2, and assuming that Xenon lamp 13 hasjust been fired to irradiate rod 10, an emitted beam leaving the end 12aof laser rod 10' will enter face 18 of rotating prism 15, thereafter toimpinge upon reflection pint l on face 20, from which the beam will bereflected to leave face 19 of the rotating prism. The beam will thenenter the vertical face 25 of stationary roof prism 24 thereafter toimpinge upon reflection point 2 which lies in the plane of the slopingface 26 of prism 24. The beam then will be deviated through a angle toimpinge upon reflection point 3 on the lower sloping face 27 of prism24, and at this point the beam will be deviated again through a 90 angleto emerge from the vertical face 25 of prism 24 and will enter thevertical face 19 of rotating prism 15. The beam then will be deviatedthrough a 90 angle (other angles of deviation could be used providedthat total internal reflection occurs at surface 20) by reflection atpoint 4 to emerge from the vertical face 18 of prism 15 and enter thevertical face 28 of prism 23. The beam is then turned by successivereflections at points 5 and 6 upon surfaces 30 and 29, respectively, toemerge from vertical face 28 of prism 23 and enter vertical face 18 ofrotating prism 15. The beam then will be reflected at point 7 on face20, emerge from vertical face 19 of prism 15, and enter vertical face 25of prism 24 to be turned 180 by successive-reflections from points 8 and9 on faces 27 and 26, respectively. The reflected beam again will emergefrom the vertical face 25 of prism 24 and enter vertical face 19 ofprism 15, reflected at point 10 on face 20 to emerge from the other face18 of prism 15 and return in a sweeping motion to end 12a of laser rod10. Shortly thereafter a giant pulse beam is emitted from partiallyreflective face 11, as indicated in FIG. 1.

By virtue of the rotation of prism 15, the beam returned in restorationof reflection will have been deviated twice the angle through which theprism has turned for each of internal reflections l, 4, 7, and by face20. Accordingly the sweep rate of the returning beam will be eight timesthe rotational rate of prism 15, and substantially complete reflectionwill be achieved only for the very short period that the returning beamimpinges on the laser rod. importantly, the Q is restored with suchrapidity as to produce a giant-pulse, the ideal condition for achievinga giant-pulse being the restoration of Q from zero to maximum in zerotime. If the Q is restored with insufficient rapidity, no giant pulsewill occur.

It will therefore be appreciated that the alternate spoiling andrestoring of the optical path occurs more rapidly than with singlemirror systems heretofore used. Also, it will be appreciated that therotational speed of the rotatable prism can be further multipliedoptically by inclusion of additional reflective prisms positioned toreflect the beam back into the rotating prism prior to return of thebeam to the laser rod.

In the interest of further describing the invention and with referenceto FIG. 4, the prisms of the optical system illustrated in FIGS. 1, 2,and 3 have been replaced generally by mirrors bearing the same referencenumerals as the corresponding prisms but with the suffix a applied.

To simplify the FIG. 4 showing, the double reflection points of prisms23 and 24 have been replaced with single reflection points for examplepoints 2 and 3 are combined as point 2, 3, points 5 and 6 as point 5, 6,and points 8 and 9 as point 8, 9.

The numbers 1 to 10 therefore correspond generally to the reflectionpoints similarly designated in FIGS. 2 and 3. In FIG. 4 the mirror a hasbeen rotated through an angle 5 and reflection points 1, 4, 7, and 10have been taken at the rotated positions of the mirror 15a.

Maximum Q, or substantially complete reflection, is obtained withreflection occurring while mirror 15a is in the illustrated non-rotatedposition. Points of reflection affording maximum Q are indicated bynumerals l" to 10", and by notation directed to mirror 24a. In theposition of mirror 15a at which maximum Q occurs, theillustrated emittedray is returned to the laser rod substantially along the same path as itleft. In terms of the reference numerals, the emitted ray first isreflected at point 1 on mirror 15a, thence impinges at point 2", 3" onmirror 24a, and is reflected back onto point 4" on mirror 15a from whichit is reflected onto point 5", 6". The ray then is caused to follow' thesame path with reflections at point 7 on mirror 15a, point 8", 9" onmirror 24a, back to point 10" on mirror 15a for return to the laser rodalong the line on which the ray was emitted. While points 1 and 1" havebeen illustrated as being substantially coincident, it will beunderstood that the point 1 will have been displaced slightly due torotation of mirror 150.

With reference to FIG. 5, mirror 24a has been folded about theillustrated rotated position of mirror 15a. In the resulting diagram,for each time the beam strikes the mirror 240 (at points 2, 3 and 8, 9)the beam is deviated 4 times the angle of rotation 8 of prism 15a. Sincethe mirror 24a is struck twice 2, 3 essentially are the same points, asare 8, 9 the total deviation is eight times the angular rotation of therotating mirror 15a. Considered another way, it can be demonstrated,using the geometry of FIG. 5, that since the normals to the mirrorthrough points 2, 3 and 8, 9 are parallel, then the total deviation isthe sum of the original angle of incidence (28) and the final angle ofreflection (66), Le. 28 68=86, as indicated on the diagram.

Since the returning beam sweeps at eight times the angular rotationalrate of the prism 15, the effective shutter operation, in restoring thereflection, occurs in a fraction of the time achieved with a simplerotating mirror optical system.

With reference to the modified embodiment of the invention illustratedin FIG. 6, laser rod 31 has a partially reflective end face 32 and asubstantially nonreflective, light transmissive end face 33. Prism 34 isrotatable about its longitudinal axis, has the cross-section of a 45 X45 X triangle, and is in optical alignment with laser rod 31, and alsowith a stationary 45 X 45 X 90 roof prism 35, and a like but smaller,stationary roof prism 36. In the illustrated position of the rotatableprism, and for the sake of convenience, the ray of light emitted fromface 33 of laser rod 31, immediately following irradiation of the same,is shown as returning along a path parallel to the path along which itis emitted in restoring the Q of the system. The light ray will travelfrom rod 31 for multiple reflections by the prisms 34, 35, and 36, andreturn to the rod 31 via the paths to which directional arrows have beenapplied. Thereafter, the giant pulse is emitted from the partiallyreflective end 32 as shown. In such an arrangement, as was the case withthe apparatus illustrated in FIGS. 1 to 5, wherein the angle ofdeviation was increased by twice the angle of prism rotation for each offour reflections by the rotating prism, the ray returning to the rod 31will have a sweep rate eight times the rotational angular velocity ofprism 34.

In FIG. 7 there is illustrated a modification of the apparatus shown inFIG. 6, the reflecting faces of the rotating prism 40 being doubled ascompared with prism 34 of FIG. 6, and the number of roof prisms beingincreased to four, as seen at 41, 42, 43 and 44. There are eightreflections by the rotating prism of this system to make the sweep rateof the emitted ray of light 16 times the prism angular velocity.

With more particular reference to FIG. 7, each of prisms 41, 43, and 44has the same configuration as prisms 35 and 36, for example, in thattheir roof surface portions lie in planes disposed at right angles toone another. The rotating prism 40 comprises two rotatably mounted pairsof 45 X 45 X 90 cross-sectional prisms 40a, 40b, 40c and 40d withhypotenuse faces spaced approximately 0.005 in. apart. The matinghypotenuse faces of one pair of prisms (40a and 4012) are disposed at aright angle with respect to the mating faces of the other pair (400 and40d).

In the interest of clarity, the rays entering and leaving the severalprisms are illustrated as travelling along the same light paths, andwill be traced by means of numbers applied to the reflection points.Starting with the ray as it leaves the laser rod following irradiation,it will first impinge at 101 upon the reflective face of prism 40a to bereflected upward for successive reflections at 102 and 103 by slopingfaces of roof prism 41. The ray leaves prism 41 to impinge at 104 uponthe reflective face of prism 400 for successive reflections horizontallyat 105 and 106 by sloping faces of roof prism 42. The ray then entersprism 40b to be reflected at 107 on its reflective face downwardly intoroof prism 43 for successive reflections at 108 and 109. The ray thentravels upwardly to enter prism 40d for reflection at 110 on itsreflective face, the ray then leaving the rotating prism to enter roofprism 44 for successive reflections at 1 11 and 112, from the slopingfaces of this prism. Since the emitted and returned rays are beingconsidered as coincident, points 111 and 112 also are coincident, andthe ray can be described as returning to the laser rod from point 112 bysuccessive return reflections at points 110,l09,l08,107,106,105, 104,103, 102, 101.

Whereas the embodiment illustrated in FIG. 6 restores reflection to thesystem, or unspoils the Q, substantially eight times faster than asimple rotating mirror, the embodiment illustrated in FIG. 7 achieves Qrestorations substantially sixteen times faster than does a simplerotating mirror.

The apparatus illustrated in FIG. 8 is similar to that shown in FIG. 6,with the exception that the prisms are so shaped and disposed that theangle A at which the light enters a prism each identified by the samereference numeral as the corresponding prism in FIG. 6, with the suffixa is the Brewster angle for the prism material. Therefore, no reflectionlosses occur at external surfaces of the prisms for light polarizationin the vertical plane, as is the light beam leaving the laser rod. Theinternal angles of reflection B are greater than the critical angle forthe prism material and hence total reflection occurs in the rotatingprism 34a. The reflection angles B in the two stationary prisms 35a and36a of the same material also are total reflections. As is the case withapparatus shown in FIG. 6, this arrangement produces an angular sweep ofthe energy returning to the laser rod at a rate 8 times the rotationalrate of the rotating prism, and is thus substantially four times asrapid in sweeping the beam as is a simple mirror.

Turning now to the modified embodiment of the invention illustrated inFIG. 9, a laser rod 51 having partially reflecting face 52 and anon-reflective face 53 is optically aligned with a rotatable planemirror 54. The optical equivalent of a telescope is interposed betweenthe non-reflective end 53 of laser rod 51 and the mirror 54, thetelescope comprising a plano-convex eyepiece lens 55 and a likeobjective lens 56, each arranged as shown. Mirror 54 and objective lens56 are of the same diameter, larger than the cross-sectional area oflaser rod end 53.

The paths of light rays emitted from and reflected onto non-reflectingend 53 of the rod 51 are indicated for convenience as travelling thesame paths in either direction, and under condition of maximumreflection. The path of the giant pulse beam is indicated by arrowsemanating from the partially reflecting face 52. While means forirradiating rod 51 has not been illustrated, it will be appreciated thatan arrangement similar to the one illustrated in FIG. 1 may be utilized.

The gain of the telescope in FIG. 9 effectively multiplies therotational rate of the mirror inasmuch as the beam width emitted by endface 53 is magnified to the width of mirror 54 for a given rotationalrate of the mirror. It follows, therefore, that if a wider reflectedbeam is swept at the angular rotational rate afforded by the roatingmirror, a resultant increase in beam velocity across the end 53 of rod51 is achieved. For example, if mirror 54 rotates at 20,000 rpm, atelescope having a gain of 5 has the effect of a smaller diameter mirrorrotating at 5 times 20,000 rpm, or l00,000 rpm.

This principle of shutter speed magnification may be set forth asfollows, using exemplary values as tabulated:

0.25 inches l0 see. are (half-angle) 24,000 rpm (400 rps) 5X 5 X 0.25 or1.25 inch Pulse Duration 10 see. are

X3600 sec. arc/degree Pulse Duration 2 X10 seconds (time) The factor (2)in the denominator represents the increase in sweep rate due to rotationof mirror 54.

In FIG. 10, the embodiment illustrated in FIG. 9 has been modifiedsubstantially by making the non-reflective end of a laser rod 61 into aconvex surface 62 and making the non-reflective surface of the rotatablemirror 63 convex as shown. This arrangement achieves the samemagnification of the rotational speed of the mirror as does theembodiment shown in FIG. 9, since the reflected beam width is againincreased to that of the rotating mirror 63.

In the apparatus of both FIGS. 9 and 10 the beams include crossoverpoints which can produce an energy concentration sufficient to ionizeair in the region thereof. This latter problem, should it arise, can beovercome by the lens arrangement illustrated in FIG. 11, in which thenon-reflective end 67 of the laser rod 66 is made concave, and therotatable mirror 68 is the same as the mirror 63 of FIG. 10. Theconcavely curved surface of laser rod 66 serves as a negative lens, andin combination with curved rotatable mirror 68 comprises a Galileantelescope.

The rotatable mirror of FIG. 11 can be also modified, if desired, totake theconcave form 68a shown in FIG. 11a, in which the concave surfaceis made reflective.

Still further modified apparatus embodying the invention is illustratedin perspective in FIG. 12 and is similar to that illustrated in FIG.11a. The primary difference is that the laser rod 71 is rectangular incross section and its concave, non-reflective end 72 projects rays ontoa similarly rectangular concave reflective face of a rotatable mirror73. In this rectangular arrangement each of the curved surfaces iscylindrical, and magnification is normal to the axis of rotation of themirror 73. An advantage of this arrangement is that the mass of therotating mirror is less than that of one with a generally sphericalreflective surface, as in the previous example.

In FIG. 12A, the rotatable mirror of FIG. 12 has been replaced with arotatable roof prism 73a provided with a convex face disposed foralignment with the concave face of the laser rod once for eachrevolution of the prism, and the light paths again are indicated bymeans of arrows.

In any of the embodiments illustrated in FIGS. 9 to 12A, the relativelylarge reflective surfaces reduce the power density at these surfaces,whereby there is less energy concentrated in the optical system. Thischaracteristic permits operation at higher energy levels without damageto reflecting surfaces.

From the foregoing description it will be appreciated that the inventionaffords means for advantageously increasing the effective speed of amechanical shutter for a laser device by optical means disposed in novelcooperative relationship with the shutter and the working element of thedevice.

I claim:

1. In laser apparatus, a working element capable of laser action andincluding a light transmissive face, reflective shutter means forreflecting radiation emitted by said working element back onto saidface, comprising a rotatable mirror disposed and operative in one of itsrotated positions to reflect radiation emitted by said element, meansfor establishing the rotational speed of said mirror, and means operableoptically to modify the operating speed of said shutter means,comprising telescope means interposed between the said face of saidworking element and said mirror, and operative to magnify the width ofthe beam reflected onto the face of said working element, said telescopemeans including an eyepiece lens of substantially the samecross-sectional area as said face and an objective lens of substantiallythe same cross-sectional area as said rotatable mirror.

2. Apparatus according to claim 1 wherein the eyepiece lens of saidtelescope is formed integrally with the light transmissive face of saidworking element, and the objective lens is formed integrally with saidrotatable mirror.

3. Apparatus according to claim 2 and characterized in that the eyepiecelens of said telescope is concave.

4. Apparatus according to claim 1 and characterized in that said workingelement is an elongated crystal generally rectangular in cross section,and the light transmissive face comprises a concave eyepiece lens forsaid telescope, said face being formed as a section of a cylinder formedabout an axis of curvature generally parallel to the axis of rotation ofsaid rotatable mirror, and said rotatable mirror being formed as acylindrical section having its axis of curvature substantially parallelwith the axis of rotation of the mirror.

5. Apparatus according to claim 1 and characterized in that the workingelement is of a generally rectangular cross section, the telescopeeyepiece being concave and formed integrally with the light transmissiveface of the working element, the objective lens being formed integrallywith the rotating mirror, said rotating mirror comprising a roof prismrotatable about an axis parallel to the centers of curvature of theobjective lens and the eyepiece lens.

6. ln laser apparatus, a working element capable of laser action,reflective shutter means for reflecting radiation emitted by saidworking element back into the latter, means for establishing theoperating speed of said shutter means, and optical means operable tomodify the operating speed of said shutter means, said apparatus beingfurther characterized in that said shutter means comprises a rotatablemirror disposed to reflect radiation by said element in one of itsrotated positions, and said optical means comprises telescope meansinterposed between said working element and said mirror and operative tomagnify the width of the beam reflected onto said working element.

7. Apparatus according to claim 6 and further characterized in that saidtelescope comprises an eyepiece lens substantially of the diameter ofthe work ing element, and an objective lens, said rotating mirror andsaid objective lens being of a diameter greater than that of the workingelement, the magnification being a function of said differences indiameters of the recited lenses.

8. In laser apparatus, a generally cylindrically shaped ruby crystalcapable of laser action having substantially planar, opposite end faceportions, one face portion having partially light reflective meansassociated therewith and the other face portion being substantiallytotally light transmissive, a source of light energy for irradiatingsaid ruby crystal to effect emission of a light beam by said other faceportion, rotatable mirror means disposed for optical alignment with saidother face portion in one of its rotated positions for returning theemitted light to said other face portion, means for rotating said mirrormeans at a predetermined rotational speed, means for intermittentlyenergizing said source of energy in substantial synchronism with therecited optically aligned position of said mirror means, and meansoperable optically to modify the apparent rotational speed of saidrotatable mirror means, said last recited means comprising meansdefining a telescope interposed between said crystal and said rotatablemirror means and operative to magnify the width of the beam of light asit is returned to said other face portion.

9. A laser generator comprising: an active laser component havingopposite ends disposed within an optically resonant cavity;

means for pumping said component so that a population inversion resultsthereby producing a negative temperature medium and means for emittingresulting laser light energy from said optically resonant cavity, saidlaser component having a first reflector proximate to one end and asecond reflector spaced from the opposite end;

means for rotating said second reflector;

means for synchronizing said pumping means and said second reflector forattaining a maximum population inversion in said laser component; and

a telescope system, said telescope system having a power greater thanunity when viewed from said laser component toward said secondreflector, said telescope system being disposed within said cavitybetween said second reflector and said opposite end.

10. A laser generator as set forth in claim 9 wherein said telescopesystem comprises a Galilean telescope system including a first negativelens and a second lens.

11. The laser generator as set forth in claim 9 wherein said secondreflector is a substantially totally reflecting prism.

12. The laser generator as set forth in claim 9 wherein said telescopesystem comprises first and second lenses, spatially disposed within saidcavity along the cavity axis by an amount equal to the sum of the focallengths of said lenses, so that the focal points of said lenses are acommon point.

13. A laser structure comprising:

a laser component providing a segament of a waveenergy propagation path;

means for energizing said component to establish an inversion of energystates and thereby produce a negative temperature medium and means foremitting resulting laser light energy from said laser component;

a first wave-energy reflector terminating a first end of saidpropagation path;

means for terminating a second end of said propagation path including asecond wave-energy reflector, rotatable to undergo angular displacementabout an axis perpendicular to the axis of said laser component into andout of position reflectively terminating said second end of saidpropagation path;

means for effecting said angular displacement of said second wave-energyreflector successively into and out of said position to control thevalue of the ratio of wave-energy storage to wave-energy dissipation perwave-energy cycle within said path for wave-energy propagation alongsaid path, and

a telescope system, said telescope system having a power greater thanunity when viewed from said laser component toward said secondwave-energy reflector, said telescope system being disposed between saidsecond reflector and said laser component.

14. The laser structure as set forth in claim 13 wherein said telescopesystem is a Galilean telescope system including a first negative lensand a second lens.

15. The laser structure as set forth in claim 13 wherein said secondwave-energy reflector is a substantially totally reflecting prism.

16. The laser structure as set forth in claim 13 wherein said telescopecomprises first and second lenses, spatially disposed along said path byan amount equal to the sum of the focal lengths of said lenses, so thatthe focal points of said lenses are a common point.

17. A laser light source comprising: a body of laser material capable ofpopulation inversion between a normal and a higher energy state;

pumping means for attaining a population inversion in the lasermaterial; two reflectors arranged to define a resonant cavity about thelaser material; means for rapidly moving one of the reflectors in suchmanner as to produce a sudden increase in the Q of the resonant cavityimmediately after a maximum population inversion has been attained inthe laser material; and characterized by an afocal magnifying opticalsystem disposed within the resonant cavity in an optical path betweenthe body of laser material and the movable reflector. 18. A laseraccording to claim 17, in which the afocal magnifying'optical systemcomprises the two lenses of a Galilean telescope.

19. A laser light source comprising: a rod of laser material such asruby;

pumping means for attaining a population inversion in that rod; tworeflectors arranged to define a resonant cavity about the said rod;means for rotating one of the said reflectors in phase with the laserpumping means so as to produce a sudden increase in the Q of theresonant cavity immediately after a maximum population inversion hasbeen attained in the rod; and characterized by the disposition of thetwo lenses of Galilean afocal telescope in an optical path between thelaser rod and the rotatable reflector. 20. A laser according to claim19, in which the rotatable reflector has the form of a roof prism and inwhich the positive and negative optical surfaces of the Galileantelescope are formed on the roof prism and on the laser rodrespectively.

1. In laser apparatus, a working element capable of laser action andincluding a light transmissive face, reflective shutter means forreflecting radiation emitted by said working element back onto saidface, comprising a rotatable mirror disposed and operative in one of itsrotated positions to reflect radiation emitted by said element, meansfor establishing the rotational speed of said mirror, and means operableoptically to modify the operating speed of said shutter means,comprising telescope means interposed between the said face of saidworking element and said mirror, and operative to magnify the width ofthe beam reflected onto the face of said working element, said telescopemeans including an eyepiece lens of substantially the samecrosssectional area as said face and an objective lens of substantiallythe same cross-sectional area as said rotatable mirror.
 2. Apparatusaccording to claim 1 wherein the eyepiece lens of said telescope isformed integrally with the light transmissive face of said workingelement, and the objective lens is formed integrally with said rotatablemirror.
 3. Apparatus according to claim 2 and characterized in that theeyepiece lens of said telescope is concave.
 4. Apparatus according toclaim 1 and characterized in that said working element is an elongatedcrystal generally rectangular in cross section, and the lighttransmissive face comprises a concave eyepiece lens for said telescope,said face being formed as a section of a cylinder formed about an axisof curvature generally parallel to the axis of rotation of saidrotatable mirror, and said rotatable mirror being formed as acylindrical section having its axis of curvature substantially parallelwith the axis of rotation of the mirror.
 5. Apparatus according to claim1 and characterized in that the working element is of a generallyrectangular cross section, the telescope eyepiece being concave andformed integrally with the light transmissive face of the workingelement, the objective lens being formed integrally wIth the rotatingmirror, said rotating mirror comprising a roof prism rotatable about anaxis parallel to the centers of curvature of the objective lens and theeyepiece lens.
 6. In laser apparatus, a working element capable of laseraction, reflective shutter means for reflecting radiation emitted bysaid working element back into the latter, means for establishing theoperating speed of said shutter means, and optical means operable tomodify the operating speed of said shutter means, said apparatus beingfurther characterized in that said shutter means comprises a rotatablemirror disposed to reflect radiation by said element in one of itsrotated positions, and said optical means comprises telescope meansinterposed between said working element and said mirror and operative tomagnify the width of the beam reflected onto said working element. 7.Apparatus according to claim 6 and further characterized in that saidtelescope comprises an eyepiece lens substantially of the diameter ofthe working element, and an objective lens, said rotating mirror andsaid objective lens being of a diameter greater than that of the workingelement, the magnification being a function of said differences indiameters of the recited lenses.
 8. In laser apparatus, a generallycylindrically shaped ruby crystal capable of laser action havingsubstantially planar, opposite end face portions, one face portionhaving partially light reflective means associated therewith and theother face portion being substantially totally light transmissive, asource of light energy for irradiating said ruby crystal to effectemission of a light beam by said other face portion, rotatable mirrormeans disposed for optical alignment with said other face portion in oneof its rotated positions for returning the emitted light to said otherface portion, means for rotating said mirror means at a predeterminedrotational speed, means for intermittently energizing said source ofenergy in substantial synchronism with the recited optically alignedposition of said mirror means, and means operable optically to modifythe apparent rotational speed of said rotatable mirror means, said lastrecited means comprising means defining a telescope interposed betweensaid crystal and said rotatable mirror means and operative to magnifythe width of the beam of light as it is returned to said other faceportion.
 9. A laser generator comprising: an active laser componenthaving opposite ends disposed within an optically resonant cavity; meansfor pumping said component so that a population inversion resultsthereby producing a negative temperature medium and means for emittingresulting laser light energy from said optically resonant cavity, saidlaser component having a first reflector proximate to one end and asecond reflector spaced from the opposite end; means for rotating saidsecond reflector; means for synchronizing said pumping means and saidsecond reflector for attaining a maximum population inversion in saidlaser component; and a telescope system, said telescope system having apower greater than unity when viewed from said laser component towardsaid second reflector, said telescope system being disposed within saidcavity between said second reflector and said opposite end.
 10. A lasergenerator as set forth in claim 9 wherein said telescope systemcomprises a Galilean telescope system including a first negative lensand a second lens.
 11. The laser generator as set forth in claim 9wherein said second reflector is a substantially totally reflectingprism.
 12. The laser generator as set forth in claim 9 wherein saidtelescope system comprises first and second lenses, spatially disposedwithin said cavity along the cavity axis by an amount equal to the sumof the focal lengths of said lenses, so that the focal points of saidlenses are a common point.
 13. A laser structure comprising: a lasercomponent providing a segament of a wave-energy propagation path; mEansfor energizing said component to establish an inversion of energy statesand thereby produce a negative temperature medium and means for emittingresulting laser light energy from said laser component; a firstwave-energy reflector terminating a first end of said propagation path;means for terminating a second end of said propagation path including asecond wave-energy reflector, rotatable to undergo angular displacementabout an axis perpendicular to the axis of said laser component into andout of position reflectively terminating said second end of saidpropagation path; means for effecting said angular displacement of saidsecond wave-energy reflector successively into and out of said positionto control the value of the ratio of wave-energy storage to wave-energydissipation per wave-energy cycle within said path for wave-energypropagation along said path, and a telescope system, said telescopesystem having a power greater than unity when viewed from said lasercomponent toward said second wave-energy reflector, said telescopesystem being disposed between said second reflector and said lasercomponent.
 14. The laser structure as set forth in claim 13 wherein saidtelescope system is a Galilean telescope system including a firstnegative lens and a second lens.
 15. The laser structure as set forth inclaim 13 wherein said second wave-energy reflector is a substantiallytotally reflecting prism.
 16. The laser structure as set forth in claim13 wherein said telescope comprises first and second lenses, spatiallydisposed along said path by an amount equal to the sum of the focallengths of said lenses, so that the focal points of said lenses are acommon point.
 17. A laser light source comprising: a body of lasermaterial capable of population inversion between a normal and a higherenergy state; pumping means for attaining a population inversion in thelaser material; two reflectors arranged to define a resonant cavityabout the laser material; means for rapidly moving one of the reflectorsin such manner as to produce a sudden increase in the Q of the resonantcavity immediately after a maximum population inversion has beenattained in the laser material; and characterized by an afocalmagnifying optical system disposed within the resonant cavity in anoptical path between the body of laser material and the movablereflector.
 18. A laser according to claim 17, in which the afocalmagnifying optical system comprises the two lenses of a Galileantelescope.
 19. A laser light source comprising: a rod of laser materialsuch as ruby; pumping means for attaining a population inversion in thatrod; two reflectors arranged to define a resonant cavity about the saidrod; means for rotating one of the said reflectors in phase with thelaser pumping means so as to produce a sudden increase in the Q of theresonant cavity immediately after a maximum population inversion hasbeen attained in the rod; and characterized by the disposition of thetwo lenses of Galilean afocal telescope in an optical path between thelaser rod and the rotatable reflector.
 20. A laser according to claim19, in which the rotatable reflector has the form of a roof prism and inwhich the positive and negative optical surfaces of the Galileantelescope are formed on the roof prism and on the laser rodrespectively.